After the latest PHP update is installed by the weekly Plesk update task, PHP scripts cannot manage session objects on sites that are configured to run PHP as CGI or FastCGI.
An update for PHP on CentOS 6 was released by the OS vendor and the weekly Plesk update process installed it. The PHP upgrade reset ownership settings and permissions on the
/var/lib/php/session directory to their default values, preventing FTP users of domains from creating files in the directory. Since CGI and FastCGI PHP scripts run based on the privileges of FTP users, this causes problems for scripts that try to create session objects.
The issue has been fixed in Plesk 11.0.9 Micro-Update #42 .
Use these commands to set proper permissions and ownership settings on
# chmod 1733 /var/lib/php/session
# chown root:root /var/lib/php/session
129051 Permissions on /var/lib/php/session/ are changed after PHP update in Plesk 12.5